Poly-alpha-olefin compositions containing dialkyl - 3,3&#39; - thiodipropionates and polyphenols



United States Patent 0.

US. Cl. 26045.85 3 Claims ABSTRACT OF THE DISCLOSURE Polyolefincompositions stabilized with a dialkyl-3,3'- thiodipropionate and apolyphenol.

This invention relates to new poly-a-olefin compositions. Preferredembodiments of the invention relate to polyethylene and polypropylenecompositions having improved stability at elevated temperatures tooxidative degradation.

Poly-a-olefins such as polyethylene, polypropylene and the like arecommonly subjected to elevated temperatures in the course of theirprocessing into useful items of commerce. Such processing methods asrolling, injection molding, extrusion and the like at elevatedtemperatures usually result in oxidative degradation of the polymer. Inaddition, many uses of poly-a-olefins, such as in electrical insulationand the like, often times expose the poly-u-olefin to elevatedtemperatures. To minimize oxidative deterioration in poly-a-olefins,anti-oxidants or stabilizers are often times incorporated therein.

It is an object of this invention to provide new poly-aolefincompositions having improved resistance to thermal degradation.

It is another object of this invention to provide new synergisticcombinations of stabilibzers for poly-a-olefin compositions.

It is also an object of this invention to provide novel polyethylene andpolypropylene compositions containing synergistic combinations ofcompounds that improve the stability of the polyethylene andpolypropylene compositions against deterioration resulting from exposureto elevated temperatures.

Other objects of the invention will be apparent from the description andclaims that follow.

The present invention comprises poly-a-olefin compositions havingincorporated therein a stabilizer combination of certain diesters of3,3'-thiodipropionic acid and polyphenols.

The diesters of 3,3'-thiodipropionic acid comprising the presentstabilizer combination have the following formula wherein R is an alkylradical having at least 4 and generally 4 to 20 carbon atoms, with 8 to18 carbon atoms being preferred. A particularly eifective ester hastwelve carbon atoms for the R substituent, namely, dilauryl-3,3'-thiodipropionate. However, any diester of 3,3'-thiodipropionic acid asdescribed above can be employed in the present stabilizer combinationincluding the butyl, amyl, hexyl, heptyl, octyl, nonyl, decyl, tridecyl,myristyl, pentadecyl, ceptyl, heptadecyl, stearyl, and icosyl diestersof 3,3-thiodipropionic acid, or mixtures thereof.

A wide variety of polyphenols can be effectively utilized in combinationwith the described diesters of 3,3-thiodipropionic acid including thosehaving the following general formula,

on ron] on Rr-om-ort R4 R1 R3 n 5 wherein R R R R and R are alkylradicals usually having 1 to 12 carbon atoms and preferably 1 to 4carbon atoms, and n is an integer of 1 to 4 and preferably 1 to 2, R andR are preferably tertiary alkyl radicals such as tertiary butylradicals. Other suitable substituents for R R R R and R include methyl,ethyl, isopropyl, nbutyl, amyl, octyl, decyl, lauryl, stearyl, andrelated alkyl radicals. Typical polyphenols of the invention include 4-rnethyl-a,a-bis 3-tert.-butyl-5-methyl-Z-hydroxyphenyl -2 6-xylenol anda W-methylenebis(2-hydroxy-5-methylm-phenylene)bis(6-tert.-butyl-2,4-xylenol). The polyphenols of the invention can beprepared by the method described in Angewandte Chemie, vol. 70, pp.390-8, July 7, 1958.

The combination of the described diesters of 3,3'-thiodipropionic acidand polyphenols can be used to stabilize a wide variety of solidpoly-a-olefin compositions against deterioration resulting from exposureto elevated temperatures. Any of the normally solid polymers of oc-mOnO-olefinic aliphatic hydrocarbons containing 2 to 10 carbon atoms can bestabilized in accordance with the invention. The subject stabilizercombinations are prefera bly used in polyethylene and polypropylene,although such poly-u-olefins as poly(3-methylbutene-1), poly(4-methylpentene-l), poly(pentene-l), poly(3,3-dimethylbutene-lpoly(4,4-dimethylbutene-1), poly(octene-1), poly(decene-1), and the likecan also be stabilized with the subject stabilizer combinations. Boththe so-called low density and high density or high crystallinitypoly-a-olefin compositions can be stabilized in accordance with theinvention. Reference is made to Fawcett et al. US. Patent No.2,153,553granted Apr. 11, 1939, and to copending applications CooverU.S. Ser. No. 559,53 6 filed Jan. 17, 1956, now abandoned, and Coover etal. US. Ser. No. 724,904 filed Mar. 31, 1958, now abandoned, with regardto the preparation of various poly-a-olefin compositions that can bestabilized against thermal degradation in accordance with the invention.The additive stabilizer combinations of the invention are especiallyuseful for stabilizing the solid resinous po'ly-a-olefins having averagemolecular weights of at least 15,000 and more usually at least 20,000,although the stabilizer combinations of the invention can also beutilized to stabilize the so-called poly-a-olefin waxes having loweraverage molecular weights of usually 3,000 to 12,000.

and about .01% to 1% of the polyphenol being preferred, theconcentration being based on the weight of the polyz-olefin. Wegenearlly utilize the combination of the subiect stabilizers at a weightratio of the diester of 3,3- thiodipropionic acid to the polyhenol inthe range of 1/ 100 to 100/l, and preferably 1/50 to 50/1.

The stabilizer combination of the invention can be ineorpoarted orblended into poly-a-olefin compositions by the conventional methodsutilized for blending such materials into resins or plastics. Typical ofsuch methods that can be suitably employed include milling on heatedrolls, deposition from solvents, and dry blending. The stabilizers ofthe invention can be incorporated separately or together into thepoly-a-olefin compositions.

The stabilizer combinations of the present invention lend topoly-a-olefin compositions improved stability, and more particularly,improved stability against oxidative deterioration resulting fromexposure to elevated temperatures. In addition, poly-u-olefincompositions contain- 'ing the stabilizer combinations of the inventionhave enhanced stability against deterioration resulting from exposure toelevated temperatures. In addition, poly-aolefin compositions containingthe stabilizer combinations of the invention have enhanced stabilityagainst deterioration resulting from exposure to sunlight or ultravioletlight. Thus, poly-u-olefins stabilized in accordance with the inventionhave an extended life expectancy and can be used more effectively thanunstabilized poly-a-olefins for a wide diversity of uses. Poly-a-olefinsstabilized as described can be cast, extruded, rolled or molded intosheets, rods, tubes, pipes, filaments and other shaped articles,including the widely used films of the polymers about .5 to 100 mils inthickness. The present compositions can be used for coating paper, wire,metal, foil, glass fiber fabrics, synthetic and natural textiles orfabrics, and other such materials.

The subject stabilizer combinations of dialkyl esters of3,3-thiodipropionic acid and polyphenol are synergistic combinations,namely, the stabilizing effect of such combinations in poly-a-olefins issubstantially greater than the additive effect of the individualstabilizers of the combination.

A minor proportionate amount of unesterified 3,3- thiodipropionic acidcan be added to the subject poly-uolefin compositions to minimize colorformation imparted by certain phenols. Usually about .005% to 3%, andpreferably about .01% to 1% by weight based on the weight of thepolyu-olefin of 3,3-thiodipropionic acid is utilized.

The invention is illustrated by the following examples of preferredembodiments thereof. In the following examples the stability of thepoly-a-olefins was determined by an oven storage test. ThepOiY-OL-OlCfin under investigation is compression molded into a smoothsheet or plate. The plate is then cut into pieces weighing about 0.25 geach. The 0.25 g. samples of the molded polymer are then placed in anair oven at 160 C. Samples are removed at intervals and each sampleanalyzed for peroxides. The oven storage life is the time required forinitial peroxide formation in a sample of the polymer. To determineperoxide formation in the oven exposed samples, each 0.25 g. sample inquestion is dissolved or suspended in ml. of carbon tetrachloride andallowed to digest for minutes. To this is added 20 ml. of a mixtureconsisting of 60% glacial acetic acid and 40% chloroform, and then 1.0ml. of a saturated aqueous solution of potassium iodide. The resultingmixture is allowed to react for two minutes, 100 ml. of water is addedto dilute the mixture, and then a starch indicator is added. Theresulting mixture is then back-titrated with 0.002 N sodium thiosulfate.The peroxide concentration, P, in milliequivalents per kilogram ofpolymer is given by the expression, P=8S, where S is the number ofmilliliters of 0.002 N sodium thiosulfate used.

EXAMPLE 1 A typical polyphenol stabilizer component of the invention wasprepared as described below. A solution of 18 g. of2,6-dimethylol-p-cresol and 36 g. of 2-tert.-butylp-cresol in 100 ml. ofn-hexane was heated with stirring on'a steam bath while dry hydrogenchloride was passed into the reaction vessel. The resulting mixture wasallowed to react about 3 hours, after which the reaction mixture wascooled and washed with aqueous sodium bicarbonate. The n-hexane solventwas evaporated to a volume of 50 ml. The resulting mixture was chilledand the resulting crystal were recrystallized from a benzenehexanemixture to give 12 g. of white crystals of the trisphenol,4-methyl-u,a-bis 3-tert.-butyl-5-methyl-2-hydroxyphenyl)-2,6-xylenol,melting 158-164 C.

A carbon-hydrogen analysis showed. Calculated: C=80.9%, H=8.70%. Found:C=80.3%, H=8.87%.

EXAMPLE 2 Several samples of powdered polypropylene were mixed withdilauryl-3,3'-thiodipropionate and a polyphenol prepared as described inExample 1, compression molded into plates inch in thickness, and theresulting molded samples evaluated with respect to stability by the 160C. oven storage test described above. The polypropylene was a plasticgrade solid polypropylene having an average molecular weight greaterthan 15,000, a density of about .91 and an inherent viscosity of about1.46 as determined in tetralin at 145 C. The results of the stabilitytest are summarized by the data set out in Table A below. Samples of theindividual components of the stabilizer combinations in thepolypropylene, as well as the polypropylene with no additive, wereincluded in the stability test for purposes of comparison. The dilauryl-3,3-thiodipropionate is indicated in the table as DLTDP. Theconcentrations in Table A are based on the Weight of the polypropylene.

Table A Oven life at Additive: 160 C., hours None 2 0.3% DLTDP 3 0.1%polyphenol 45 0.1% polyphenol +0.3% DLTDP 0.2% polyphenol 0.2%polyphenol +0.3% DLTDP 175 4methyl-a,a-bis(3-tert.-buty1-5-methyL2-hyroxyphenyl)- 2,6-xylenol. Ascan be observed from the data set out in the above table, the subjectstabilizer combination gives a stabilizing effect in polypropylene thatis greater than the additive eflect of the individual componentscomprising the combination. Similar synergism is demonstrated if plasticgrade solid polyethylene having an average molecular Weight greater than15,000, a density of about .91 and a melt index of about 7.59 issubstituted for the polypropylene as the poly-a-olefin in the describedevaluations.

EXAMPLE 3 Several samples of plastic grade solid polypropylene having anaverage molecular weight greater than 15,000, a density of about .91 andan inherent viscosity of about 1.74 as determined in tetralin at C.containing stabilizers of the invention were evaluated with respect tostability by the C. oven storage test as described in Example 2 above.Combinations of dilauryl-3,3'-thiodipropionate wtih4-methyl-a,rx-bis(3-tert.-butyl-5-methyl-2-hydroxyphenyl)-2,6-xylenoland a ,u -methylenebis (2-hydroxy-S-methyl-m-phenylene)bis(6-tert.-butyl2,4- xylenol) were evaluated. The results of the stability test aresummarized by the data set out in Table B below. In Table B,dilauryl-3,3'-thiodipropionate is indicated as DLTDP, 4 methyla,a'-bis(3-tert.-butyl-5-methyl-2- hydroxyphenyl)-2,6-xylenol isindicated as polyphenol A, and a ,a-methylenebis(Z-hydroxy-S-methyl-m-phenylene)bis(6-tert.-butyl-2,4-xylenol)is indicated as polyphenol B. The concentrations in Table B are based onthe weight of the polypropylene.

Similar synergism as that demonstrated above in Table B is demonstratedif plastic grade solid polyethylene having an average molecular weightgreater than 15,000, a density of about .91 and a melt index of about7.59 is substituted for the polypropylene as the poly-a-olefin.

The present invention thus provides novel poly-a-olefin compositionshaving improved stability against deterioration resulting from exposureto elevated temperatures, and particularly, it provides novelsynergistic stabilizer combinations for poly-a-olefin compositions.

Although the invention has been described in detail with reference topreferred embodiments thereof, it will be understood that variations andmodifications can be eifected within the sipirt and scope of theinvention as described hereina-bove and as defined by the appendedclaims.

Iclaim:

1. A polymeric composition comprising (A) a poly-a-olefin derived froma-monoolefinic hydrocarbons having 2 to carbon atoms, and

(B) a stabilizing amount of a stabilizer combination comprising (1) adialkyl ester of thiodipropionic acid wherein the alkyl moieties eachhave 4 to carbon atoms, and

6 (2) a polyphenol having the following formula or: on on OH RQQH'QCHUCmO-R I I w R R3 R5 wherein R R R R and R are alkyl radicalshaving 1 to 12 carbon atoms. 2. A polymeric composition according toclaim 1 wherein said poly-a-olefin is polypropylene. 3. A stabilizercombination comprising (A) a dialkyl ester of thiodipropionic acidwherein the alkyl moieties each have 4 to 20 carbon atoms, and (B) apolyphenol having the following formula wherein R R R R and R are alkylradicals having 1 to 12 carbon atoms.

References Cited UNITED STATES PATENTS 2,519,755 8/1950 Gribbins26045.85 2,568,902 9/1951 Thompson et al. 26045.85

FOREIGN PATENTS 8,973 10/1956 Great Britain.

JAMES A. SEIDLECK, Primary Examiner. H. E. TAYLOR, Assistant Examiner.

US. Cl. X.R.

